A quick review about the recent and future development of the offshore wind industry and the installation methods for bottom-fixed and floating wind turbines will be given first. Challenges related to installation of ultra large wind turbine blades and foundations in deeper waters will be presented. Then, the recent work at NTNU on numerical modelling and analysis for wind turbine blade installation considering jack-up and floating vessels will be presented. The focus will be given to the determination of operational sea state limits using response-based criteria for planning of installation operations and the consideration of installation automation, sea state forecast and their effects on the installation efficiency during the execution of marine operations.